This application claims the priority of German patent document 101 05 889.6, filed 9 Feb. 2001 (PCT International Application No. PCT/EP01/15294, filed 22 Dec. 2001), the disclosure of which is expressly incorporated by reference herein.
The invention relates to a method for determining the fill quantity of an operating medium, such as engine oil, in a motor vehicle.
German patent document DE 19602599 A1 discloses a method for determining a quantity of fluid (in particular the quantity of engine oil) in a motor vehicle. The fill level of the fluid, which is sensed by means of the fill level sensor, fluctuates as a function of the driving state, which adversely affects the determination of the quantity of fluid. In order to reduce the influence of the fluctuations in the fill level, which occur in particular in the driving mode, variables that are indicative of the driving state are sensed and used to determine the instantaneous driving state. The fill level of the fluid is then sensed during selected driving states, and is used to determine the fill quantity of the fluid. This determination is carried out by reference to a known dependence of the fill level of the fluid on the fill quantity of the fluid and on the driving state.
A precondition for the start of the method is that the temperature of the fluid and the ignition status of the speed satisfy fixed conditions. The sensed fill level value is filtered digitally, as a result of which brief fluctuations in the fill level are eliminated. Furthermore, when the quantity of engine oil is determined, the engine speed is taken into account. Further variables, such as the speed of the vehicle, the temperature and the mileage reading can also be taken into account in the determination of the quantity of engine oil; moreover, statistical averaging of the measured values further increases the reliability of the determination of a quantity of fluid.
If the vehicle is inclined (for example due to uphill travel), the fluid reservoir container is inclined to the same degree and a fluid level which frequently differs from the fluid level of a horizontal vehicle is obtained on the fill level sensor, depending on the location where the fill level sensor is installed. If the quantity of fluid is determined from the measured fluid level without taking into account the angular position of the vehicle, an incorrect result may be obtained.
German patent document DE 40 42 472 C2 discloses an arrangement for determining the quantity of engine oil by measuring the engine oil level and measuring the angular position of the vehicle. For each predefined quantity of engine oil there is a uniquely defined relationship between the angular position of the vehicle and the oil level in the engine, which is utilized to infer the quantity of engine oil. The angular position of the vehicle is sensed using an angle measuring device, and the quantity of engine oil is calculated by means of a data processing device using the angular position of the vehicle. The actual angular position and/or measured angular position of the vehicle relate to the gravity field of the earth. The two variables, inclination of a vehicle and the gradient (longitudinal inclination) of a road, also relate to this, moreover.
In another method for determining the fill quantity of the operating medium, the fill level of the operating medium is sensed at two or more locations in the reservoir container of the operating medium. Even when the angular position of the vehicle is unknown, the fill quantity can be calculated from the sensed fill levels, since the fill levels for each angular position are in a fixed relationship to one another which depends on the location where the fill level sensors are mounted and on the geometry of the reservoir container. However, in order to carry out this method at least two fill level sensors are necessary. Using two fill level sensors it is possible to determine the angular position of the vehicle in the direction of the line connecting the two sensors. Furthermore, using three or more fill level sensors which are not arranged in a row it is possible to determine the angular position of the vehicle in any desired direction, that is to say even in the direction of the longitudinal axis of the vehicle and transversely with respect to the longitudinal axis of the vehicle.
One object of the present invention is to provide an improved method for determining the fill quantity of the operating medium, using only one fill level sensor.
This and other objects and advantages are achieved by the method according to the invention, in which the sensed fill level of the operating medium is corrected by means of a plurality of parameters that are used by a data processing device to determine the fill quantity of the operating medium. A fill level sensor is provided for sensing the fill level in the reservoir container of the operating medium. Operating states of the vehicle are sensed as further parameters and made available to the data processing system. Examples of these operating states are the temperature of the operating medium and the engine speed.
In order to correct the influence of the instantaneous road gradient on the sensed engine oil level, a parameter is sensed which constitutes a measure of the gradient (longitudinal inclination) of the road. The engine load, for example, becomes larger when traveling uphill as the gradient increases, and decreases when traveling downhill as the gradient increases. According to the invention, the gradient of the road is inferred from a characteristic variable for the engine load, and the engine oil level is corrected by means of the gradient of the road. In order to supplement the engine load parameter, vehicle-movement-dynamic variables may be used which give an indication of the gradient of the road traveled on. An advantage of the method according to the invention is that the fill quantity of the operating medium is determined more precisely and reliably without additional expenditure on sensors.
In one refinement of the method, the position of the accelerator pedal is sensed as the characteristic variable for the engine load, which is used to determine the fill quantity of the operating medium. Accelerator pedal position is a variable which acts directly on the power generation of the engine and is thus characteristic of the load of the engine. Moreover, it is also already available as a signal on a data bus.
In another refinement of the method, the throttle valve position is used as the characteristic variable for the engine load. In many vehicles, this variable is also available on a data bus in the vehicle.
In an alternative refinement of the method, a physical variable such as force, torque or power on the drive train (that is, between the engine and the wheel), is sensed as the characteristic variable for the engine load. Such a variable is a direct measure of the engine load.
The method according to the invention can be used in particular to determine the fill quantity of fluids in reservoir containers in the vehicle, for example gear oil, brake fluid, coolant or fuel.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.